1. Technical Field
The present invention relates to an integrated coal gasification combined cycle plant, in particular, of the dry-coal-fed air-blown type.
2. Description of the Related Art
In general, a dry-coal-fed air-blown integrated coal gasification combined cycle plant is configured such that coal is supplied from a raw coal bunker to a coal pulverizer, where the coal is pulverized. The coal which has been pulverized (hereinafter referred to as “pulverized coal”) is collected by a pulverized-coal collector and is supplied to a gasification furnace via a pulverized-coal bin and a pulverized-coal hopper.
When pulverized coal is to be supplied from the pulverized-coal hopper to the gasification furnace, the pulverized coal is carried to the gasification furnace using nitrogen gas, which is inert gas separated from air by an air separation unit. Oxygen separated from air by the air separation unit is introduced to the gasification furnace, where the pulverized coal carried by the nitrogen gas is burned. The pulverized coal is partly burned and decomposed by heat in the gasification furnace and is thereafter gasified into raw syngas.
Char contained in the raw syngas which is produced is separated from the syngas through a filter. The char separated by the filter is recovered into the gasification furnace and is burned together with the pulverized coal. At that time, the char is carried to the gasification furnace by the nitrogen gas generated by the air separation unit. The filter that separates the char is prevented from clogging by backwashing using the nitrogen gas generated by the air separation unit.
The syngas that has passed through the filter is introduced to a gas turbine as fuel gas after sulfur compounds, nitrogen compounds and so on contained therein are removed by a gas purification system. The fuel gas introduced to the gas turbine is burned in a combustor of the gas turbine together with air to become exhaust gas.
The exhaust gas is exhausted from the combustor to rotationally drive the turbine of the gas turbine. Since the turbine is rotationally driven, a compressor provided coaxially therewith is rotationally driven to compress air. Electrical power is generated by a generator connected to an end of the rotating shaft. The air that the compressor has compressed is supplied to the combustor of the gas turbine and the gasification furnace.
The exhaust gas that has rotationally driven the turbine is introduced to an exhaust-heat recovery boiler. The exhaust gas introduced to the exhaust-heat recovery boiler vaporizes water introduced to the exhaust-heat recovery boiler depending on the amount of heat in the exhaust gas. The steam generated in the exhaust-heat recovery boiler rotationally drives a steam turbine mounted on the rotating shaft of the gas turbine. The rotating shaft connected to the steam turbine is further driven by rotational driving of the steam turbine. Thus, the generator is driven by the gas turbine and the steam turbine to achieve combined-cycle power generation, thus improving the power generation efficiency.
On the other hand, the exhaust gas that has given up its heat to the feed water in the exhaust-heat recovery boiler is exhausted outside the integrated coal gasification combined cycle plant through a chimney.
Moreover, part of the exhaust gas let out from the gas turbine is introduced to the coal pulverizer. The exhaust gas introduced to the coal pulverizer, because it is dry and has a large quantity of heat, is used to dry the coal supplied from the raw coal bunker.
The use of carbon dioxide exhausted from the foregoing integrated coal gasification combined cycle plant, as described above, is disclosed in Japanese Unexamined Patent Application, Publication No. Hei 4-1428, in which exhaust gas let out from a gas turbine is recovered and is circulated in a combustor of the gas turbine and a compressor.